Alternating-current relay



Nov. 26, 1929. 4 M. ALMQUIST 1,736,316

ALTERNATING CURRENT RELAY Filed March 25, 1927 INVENTOR.

A TTORNEYS.

Patented Nov. 26, 1929 UNITED STATES PATENT OFFICE MILTON L.

ALIQUIST, OI BROOKLYN, NEW YORK, ASSIGNOBDTO AIEBICAN TELEPHONE I AND TELEGRAPH COMFANY, A CORPORATION OF NEW YORK ALTEBNATING-CURBENT RELAY Application and arm as, 1927.- Serial in. 177,747.

quency, or when the frequency of the lattercurrent lies anywhere between definite limits. A selective arrangement may be interposed between the polar or alternating current relay and the direct current relay, which will tend to prevent the false operation of 'the direct current rela due to the presence of extraneous or inter ering currents impressed upon the winding of the polar or alternating current relay.

While this invention will. be ointed out with particularit in the appende claims, the invention itself, 0th as to its further ob'ects and features, will-be better understood rom the detailed description hereinafter following, when read in connection with the accompan ing drawing, showing one embodiment of t e invention merely for the purpose of illustration.

Referring to the drawing, the winding of a polar oralternating current relay is designated by the reference character W winding W being connected through leads L to a source of current of signaling frequency. The polar or alternating current relay has an armature A which is free to vibrate between contacts 1 and 2 on either side thereof. Armature A may, if desired, rest initially against either of these contacts. When alternating current from the source is applied to the winding W of the polar or alternating current relay through the leads L the armature A will v1 rate between the contacts 1 and 2 alt-the fr uenc of the current applied.

e winding of the direct current rela is designated by the referencecharacter I this direct current relay having-an armature A, and contacts 3and 4 on either side thereof. When the armature A closes contact 3, an output circuit connected to the leads L will be closed, and when the armature A moves away from contact 3, the output circuit connected to the leads L, will be opened.

Two condensers, G and C are provided inv this system, condenser C bein connected directly in series with a resistance and an mductanceL,abatteryBbeingalso provided for charging these condensers. The condenser C2 is connected directly across the windin W of the direct current relay and is of a su ciently large capacity so that upon discharge through said winding it may maintain the direct current relay operated for a definite and predetermined interval of time, as will be described more fully hereinafter. The inductance L is located in the circuit in series with the condenser C to provide a series resonant circuit exhibiting very low reactance at any frequency within predetermined limits, the net magnitudes of the inductive and capacitative reactances in the circuit including the inductance L and condenser 0 being modified somewhat by the inductance of the winding W and the capacity of the condenser C respectively. Resistance- R is connected in series with inductance L and condenser C in order to control the degree of selectivity to be provided by the circuit. In other words, the

magnitude of resistance B may be employed to control the width of the band of frequencies at which the direct current relay will operate and remain operated.

When the armature A of the polar or alternating current relay vibrates with sufiicient amplitude, it will alternately make contacts 1 and 2. When contact 1 is made by armature A,, condensers C and C, will be charged from the battery B, the char ing circuit including the battery B, the W111 'ng of the direct current relay W and the condenser C: in shunt therewith, the inductance L, the resistance R, the condenser C the armature A, of the polar or alternating current relay, contact 1 and ground. Under normal operatin conditions, the charging curcurrent relay and to maintain it operated only for a brief period of time. As the direct current relay is operated, the armature A is attracted, closing the output circuit connected to the leads L Condenser C being in shunt with the winding W of the direct current relay discharges through the winding W of this relay, causing the relay to remain operated, condenser C being also of sufficiently high capacity so that the direct current relay will remain operated for the time required for the armature A of the polar or alternating current relay to move from contact 1 to contact'2 and back-t0 contact 1, par-' ticularly when current of the proper frequency is impressed upon the winding W of the polar or alternating current relay.

When the armature A of the polar or alternating current rela closes contact 2, condenser C will be disc arged through the resistance R and the inductance L, the discharge circuit including the condenser C the resistance R, the inductance L, contact 2 and armature A of the polar or alternating current rela It will be ap arent that the discharge 0 the condenser 5 through the winding W of the direct current relay ordinarily takes place after armature A of the polar or alternating current relay has moved away from contact 1. Thereafter the armature A acgain closes contact 1, charging condensers 1 and C and so it continues. It will be observed that the windin W of the direct current relay is energize partly by the flow of current from battery B upon charge, and partly by the flow of current upon discharge of condenser 0,. It will also be apparent t at the direct current relay will remain energized as long as the armature Ag of the polar or alternatingrcurrent relaycort-"F tinues to move between contacts 1 and 2 in response to the flow of current through windmg W of proper frequency.

One of the features of this invention is that the time constant in the charging cir-' cuit is substantially equal to the time constant in the discharging circuit. In other words, the time required to charge condensers C and O to their groper values by their connection to battery is substantially the same as the time requ red forthe condenser to discharge through the circuit includingche resistance R, the inductance L and the armature A In the particular circuit described the time constants in the chargnig and dis-. charging circuits may be made substantially equal b making the capacity of the condenser 2 large as compared to the capacity of the condenser C Another feature of this invention is that the circuit arrangement interconnecting the polar or alternating current relay and the direct current relay is of the selective type; The charging circuit is in effect a series resonant circuit in which resistance is interposed to control the sharpness of the resonant property of the circuit. In a simple series circuit containing nothing more than inductance and capacity there is a definite value of frequency for which the total reactance in the circuit is zero, and at this frequency the impedance of the circuit is exactly the same as the resistance of the circuit. This frequency is generally known as the frequency of resonance, and the series circuit is then said to be in a condition of resonance at this frequency. The impedance of the series circuit at the frequency of resonance has its smallest value, the value being equal to the resistance in the circuit, and the current which flows in the circuit at .the frequency of resonance has its greatest Value. In the circuit arrangement described herein for illustrative purposes, the condenser C the resistance R, the inductance L and the winding W and condenser C in parallel therewith provide a modified form of the series resonant circuit above mentioned. This circuit exhibits negligible reactance at frequencies between definite and predetermined limits. These limiting frequencies may be chosen so that the direct current relay will be operated and remain operated only when the frequencies of the currents impressed upon the winding W of the polar or alternating current relay lie therebetween. In other words, the direct current relay will not be operated if the frequency of the current impressed upon the winding W of the polar or alternating current relay is outside of the above mentioned limits. Thus the provision of a circuit including inductance and capacity interconnecting a polar or alternating current relay and a direct current relay will introducev selectivit and. will prevent the system from respon in until the proper frequency characteristics ave been established.

If the frequency of the current impressed upon the winding .W of the polar relay is above the u per of the predetermined limits, condenser 1 will not be given sufiicient time to properly charge .and discharge, its rate of charge and discharge being controlled primarily by the inductance L. The direct current relay will then not receive sufiicient current and may not operate and stay operated. On the other hand, if the frequency of the current impressed upon the windin W is;

below the lower of the predetermine limits, condenser C will, upon discharge, be unable to maintain sufiicient current through the winding W of the direct current relay, and I hence the latter relay will not be maintained in an operative condition. However, when the frequency of the current impressed upon the winding W of the polar relay is of a suitable value, i. e., if this frequency. lies between the above-mentioned predetermined limits, condenser 0 will become charged and discharged at the proper rate, and then the voltage built up across this condenser may become higher than the normal operating voltage of battery B due to the well known resonance eifects. Clearly, this latter condition will result in considerable frequency discrimination.

While this invention has been shown and described in one particular embodiment merely for the purpose of illustration, it. will be distinctly understood that the general principles of this invention may be applied to other and widely varied organizations without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is: v

1. The combination of a polar relay the winding of which is'connected to an alternating current source and the armature of which may vibrate between two contacts, a direct current relay, and a selective circuit having a predetermlned natural period interconnecting the armature of the polar relay and the winding of the direct current relay, said selective circuit including inductive and capacitative reactance elements of predetermined magnitudes, said selective circuit permitting the direct current relay to be operated and to remain operated when current of said predetermined period is applied to the winding of said polar relay by said alternating current source and preventing the operation of said direct current relay when such current is not impressed upon the winding of said polar rela 2. The combination of a polar relay the winding of which is connected to an alternating current source, a direct current relay, and means including a tuned circuit interconnecting the polar relay and the direct current relay for operating the direct current relay and for maintaining it operated when current of the source impressed upon the winding of the polar relay has a frequency corresponding to the natural period of said tuned circuit. 0

3. The combination of a circuit carrying an alternating current, an alternating current relay the winding of which is connected to said circuit, an armature for said alternating current relay arranged to be vibrated L when said relay is energized by the alternating current flowing in said circuit, contact members on either side of said armature,

a direct current relay, a first condenser, a second condenser, an inductance, and a source of direct current, the armature of said alternating current relay, the first condenser, the inductance,'the second condenser and the source of direct current being serially connected when the armature of the alternating current relay closes one of said contact members the second condenser being connected across the winding of the direct current relay, the first condenser and the inductance being connected serially when the armature of the alternating current relay closes the other of said contact members.

4. The combination of a polar relay the winding of which is connected to an alternatmg current source, the armature of said polar relay being free to move between two contact members, a direct current relay, first and second condensers, an inductance, and a source of direct current, said condensers, the inductance and the source of direct current being serially connected when the armature of the polar relay closes one of said contact members, the first condenser and the inductance being serially connected when the armature of the polar relay closes the other of the contact members, the second condenser being connected across the winding of the direct current relay.

5. The combination of an alternating current relay, the armature of the alternating current relay being free to vibrate between two contact members, a direct current relay,

a tuned circuit comprising inductance and a capacity, and a source of direct current, said tuned circuit being connected through the.

is free to move between two contact members, first and second condensers, a resistance, an inductance, a direct current relay, and a source of direct current, the condensers, the resistance, the inductance and the source of direct current being serially connected when the armature closes one of said contact members whereby said condensers may become charged, the charging current operating the direct current relay, the first condenser being discharged through the resistance and the inductance when the armature closes the other of said contact members, the second condenser maintaining the direct current relay operated during the time required for said armature to move back and forth between said contact members.

In testimony whereof, I have signed my name to this" specification this 19th day of March, 1927. v

MILTON L. ALMQUIST. 

